Tonight I updated to the latest version of PlatformIO (2.8.6) and it appears that SPIFFS has now broken in my project (although no code changes were made).
Upon investigation, I found the following situation, which I’ve described upstream at esp8266:
The effect of this is that if you currently write files to SPIFFS without prepending a common char to the filename - i.e. “/” - you cannot get a list of “all files” in the SPIFFS subsequently.
So with the one-liner fix above, this is fixed - openDir("") returns a list of ‘all files, whatever the prefix’.
(Thought this might be of use …)